Additive Manufacturing (AM) is a production technology that is transforming the way all sorts of things are made. AM makes three-dimensional (3D) solid objects of virtually any shape from a digital model. Generally, this is achieved by creating a digital blueprint of a desired solid object with computer-aided design (CAD) modeling software and then slicing that virtual blueprint into very small digital cross-sections. These cross-sections are formed or deposited in a sequential layering process in an AM machine to create the 3D object. AM has many advantages, including dramatically reducing the time from design to prototyping to commercial product. Running design changes are possible. Multiple parts can be built in a single assembly. No tooling is required. Minimal energy is needed to make these 3D solid objects. It also decreases the amount waste and raw materials. AM also facilitates production of extremely complex geometrical parts. AM also reduces the parts inventory for a business since parts can be quickly made on-demand and on-site.
Several different techniques that use polymers have been developed for AM. These include material extrusion processes such as fused filament fabrication as well as powder bed fusing processes such as laser sintering.
Laser sintering is a process by which a three dimensional article may be formed in a layer-wise fashion by selectively projecting a laser beam having the desired energy onto a bed of resin particles. Prototype or production parts may be efficiently and economically produced by this process, which is often times referred to as selective laser sintering. This process has been described in U.S. Pat. Nos. 4,944,817; 5,516,697 and 5,382,308 to Bourell, et al.; U.S. Pat. Nos. 5,304,329 and 5,342,919 to Dickens, Jr. et al. and U.S. Pat. No. 5,385,780 to Lee.
In the laser sintering process, a high power laser is used to fuse polymer powders of the required material type together into the desired three-dimensional shape. SLS processes require a polymer powder of well-defined shape, size and composition in order to make high quality part. The preferred size of the particles is usually below 100 um (Ref: Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications Jul. 1, 2004 vol. 218 no. 3 247-252) and a narrow distribution of particle sizes is also preferred to get optimum precision and density of the sintered part. In addition, for good stacking of the powder particles, it is important that they have a regular, reproducible shape, like spherical morphology. However, the preparation of such powders from thermoplastic resins on an economic, large scale is not straightforward.
Most of the thermoplastic powders used for powder bed fusion processes such as laser sintering are made by (cryogenic) milling and subsequent sieving. This method has the disadvantage that the distribution in particle size is relatively high and that it is difficult to control the exact size of the powder. Also, fines are generated that cannot be used in the SLS process. Finally, the shape of the powder particles is very irregular.
Recently, Sumika Enviro Science has published a patent (Japanese published patent No. JP05288361B2) that describes a method to make spherical polyamide particles for laser sintering. The spherical polyamide particles are polymerized in an aqueous medium maintaining the shape of the spherical particles. Disadvantage of this method is that it seems not possible to add additives such as colorants, flow agents and the like into the particles. However, this reference does not teach or suggest this process would be useful with any thermoplastic polymers that have high glass transition temperatures (Tg). Also, polyamides have low glass transition temperatures (i.e., below 100 degrees C.)
There is still a need to provide suitable thermoplastic polyetherimide powder that can be used in powder bed fusion processes. The present invention offers a solution to that problem.